1. Field of the Invention
The present invention relates to a Josephson effect field-effect transistor wherein the active layer, made of a semiconductor material, is deposited on a layer of superconductive material.
The Josephson effect is an effect, related to superconductors, by which a superconductive current or supercurrent may exist in a semiconductor by an effect of proximity with a superconductor.
Components based on a superconductive effect will certainly find numerous applications in the near future. Their low heat dissipation associated with a very high switching speed means that they are especially promising for large-scale integrated logic circuits of the LSI or VLSI type.
2. Description of the Prior Art
Several models of field-effect transistors using the Josephson effect (JOFETS) have been described, in particular by A. W. Kleinsasser et al. in S. Ruggiera and D. Rudman ed. Superconducting Devices, Academic Press, 1990. This is a field-effect transistor with an architecture that is quite standard. Its source and drain metallizations are made of superconductive materials. The semiconductor channel bears a superconductive current (modulated by the gate) owing to the above-mentioned proximity effect.
However, one of the chief drawbacks of these types of transistors comes from the small length of coherence of the superconductivity in semiconductor materials, namely the length on which the proximity effect is exerted. To obtain significant supercurrents, it is necessary to have extremely small channel lengths, for example, of the order of 10 to 1000 angstroms or 0.1 .mu.m. With current technologies of masking, even by electron or X-ray beams, there is no known way of making a transistor wherein the source and the drain are at a distance of 0.1 .mu.m from each other and, in addition, with a gate metallization between the two metallizations, namely the source and drain metallizations.
This is why the characteristics of the JOFETs according to the prior art are not good enough to be useful.